1. Field of the Invention
The present invention relates to an apparatus and method for searching structured documents for a document structure contained therein, utilizing synonyms of tags.
2. Description of the Related Art
Extensible Markup Language (XML) is widely utilized as means for describing data. Documents written using XML is called XML documents. XML documents are known as structured documents represented in a logical tree structure using tags. The XML documents contain document structures (logical structures). In a document search for searching for such a document structure, a detailed search is possible by a search request based on the document structure. This search can realize a search of a higher accuracy than a keyword search, and provides only data users would like to use. Further, in these years, a technique (prior art) has been proposed for searching at high speed an XML document for a desired structure portion, utilizing a structure index (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-147933).
Assume here the case where a plurality of tags expressed in different ways and having the same meaning are simultaneously searched for, using structure designation information, called an XPath scheme, for designating an arbitrary document structure. In this case, it is necessary to connect a plurality of expressions having the same meaning, using an operator “|” or a logical operator “or”. Therefore, search omission will occur unless all synonyms of tags as search targets are accurately determined and contained in the structure designation information. Furthermore, if all synonyms are contained in the structure designation information, this information (XPath scheme) becomes very complex.